Hi David,

Thanks for this!

First, the middle main bullet on slide 7 should use congruence instead of
= , I think?

Second, I had a bit of a hard time following what was being used exactly.

Specifically, I had to find a copy of the book to find out that "IFS"
stands for "inner five segments [configuration]", i.e., a triangle  acd
with  b  on  ac , together with a congruent  a'c'd'  with  b' .

But working through the proof, it seems that all that is _really_ being
used, is that  abc ~ a'b'c'  implies  ab ~ a'b'  and  bc ~ b'c' (which
directly follows from the definition of congruence).

So (1) using IFS here seems kind of heavy and indirect machinery; but given
that the goal is to follow the book closely, (2) a definition would help
(with picture? e.g. Abb. 11 from page 34, but without the dotted lines).

Thanks again!

-Marnix

Op vr 17 jul. 2020 05:11 schreef David A. Wheeler <[email protected]>:

> My thanks to everyone for their constructive criticism on my draft
> prresentation on Schwabhauser 4.6! I've fixed everything I know
> about, and added another slide to briefly explain the key theorems/axiom
> the proof depends on.
>
> The new draft video is here:
> https://youtu.be/sNXgTh-8OhQ
>
> Any last-minute comments before I post it "officially"?
>
> --- David A. Wheeler
>
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